1. Field of the Invention
The present invention relates to a zoom lens barrel assembly.
2. Description of the Related Art
In conventional zoom lens barrel assemblies, two types of mechanisms have been used for causing the lens-supporting barrel provided at the front of the lens barrel assembly to extend: linear telescopic mechanisms that function via helicoids and lead cams, and non-linear mechanisms that function via cams.
A zooming optical system proposed in Japanese Patent Application No. Hei 11-79572 is constructed based on a two-lens group optical system including a front lens group and a rear lens group. In this optical system, the front lens group includes a first sub-lens group and a second sub-lens group that are provided in a lens-supporting barrel and are moved relative to each other to switch between a wide-angle photographing range and a telephoto photographing range. Accordingly, the optical system achieves widely variable focal lengths. When it is desired to further reduce the size of the zooming optical system, the length of each lens barrel can be reduced and the number of telescopic barrels may be increased. However, reduction in the length of each lens barrel considerably reduces the rotation angle of a helicoid required to extend the lens barrel, and as a result, curvature of the cam ring becomes undesirably large. This makes the design of the cam grooves complicated. Furthermore, smooth movement of the lens barrel may be interrupted due to a large variation in the torque which occurs when the lens barrel is extended.
The present invention provides a zoom lens barrel assembly which includes lens groups separated by a distance which is switched between a short focal length range and a long focal length range and can ensure smooth telescopic movement of lens barrels.
For example, in an embodiment, a zoom lens barrel assembly is provided, including a first lens group including a first sub-lens group and a second sub-lens group which move integrally during zooming; a second lens group, the first and the second lens groups moving relative to each other along the optical axis during zooming; a sub-lens group switching mechanism for moving one of the first and the second sub-lens groups away from the other of the first and second sub-lens groups in a short focal length photographing range and toward the other of the first and second sub-lens groups in a long focal length photographing range; and a zoom cam mechanism having a front lens group cam groove and a rear lens group cam groove for moving the first lens group and the second lens group toward and away from each other during zooming. The rear lens group cam groove includes a first portion corresponding to the short focal length photographing range and a second portion corresponding to the long focal length photographing range, the first and the second portions connected to each other via a discontinuous portion. The front lens group cam groove includes a non-linear portion which corresponds to the short focal length photographing range and provides a non-linear path, and a linear portion which corresponds to the long focal length photographing range and provides a linear path.
It is desirable for the linear portion of the front lens group cam groove to be aligned with a tangent of the non-linear portion at an end of the non-linear portion which corresponds to the long focal length side of the short focal length photographing range.
The discontinuous portion of the rear lens group cam groove can be constructed so that the first portion causes the second lens group to move toward the first lens group and the second portion causes the second lens group to move away from the first lens group.
It is desirable for a lead angle of the linear portion of the front lens group cam groove to extend parallel to the slope of a tangent of the non-linear portion of the front lens group cam groove.
It is desirable for the discontinuous portion of the rear lens group cam groove to correspond to an intermediate focal length photographing range which lies between the short focal length photographing range and the long focal length photographing range, wherein the discontinuous portion is not used in a photographing operation.
The zoom lens barrel assembly can include a multi-stage-extension zoom lens barrel assembly which extends and retreats between a first position and a second position, the first position and the second position corresponding to a short focal length extremity and a long focal length extremity, respectively. The multi-stage-extension zoom lens barrel assembly extends out from the most retracted position thereof by a predetermined amount to the first position and extends to a maximum position to corresponding to the second position, the discontinuous portion of the rear lens group cam groove corresponding to an intermediate focal length photographing range which lies between the short focal length photographing range and the long focal length photographing range and is not used in a photographing operation.
The sub-lens group switching mechanism can be mounted on a shutter unit secured to a frontmost barrel of the zoom lens barrel assembly, wherein the sub-lens group switching mechanism moves the first sub-lens group away from the second sub-lens group in the short focal length photographing range to bring the first and second sub-lens groups into a mutually distant position on the short focal length side, and wherein the sub-lens group switching mechanism moves the first sub-lens group toward the second sub-lens group on the long focal length photographing range to bring the first and second sub-lens groups into a mutually close position on the long focal length side.
The sub-lens group switching mechanism can include a first lens frame and a second lens frame supporting the first sub-lens group and the second sub-lens group, respectively, and a lens frame shift mechanism for moving the first and the second lens frames toward and away from each other along the optical axis and moving the lens frames integrally along the optical axis according to a rotation of a bi-directional motor mounted on the shutter unit.
The shutter unit can be secured to the frontmost barrel of the zoom lens barrel assembly. The frontmost barrel advances and retreats along the optical axis, without rotating, while following the front lens group cam groove of the zoom cam mechanism. The second lens group is supported in the rear lens group frame, which advances and retreats along the optical axis, without rotating, while following the rear lens group cam groove of the zoom cam mechanism.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 2001-82094 (filed on Mar. 22, 2001) which is expressly incorporated herein by reference in its entirety.